Thanks for the feedback. My plan will be to (1) make sure I grade the excavated area to match the patio surface (i.e., 1/4 in. per foot sloping away from the house, (2) install geotextile cloth b/w the clay soil and the gravel baselayer, (3) potentially install a drainage pipe on the low end if I get worried enough about it. And, zedosix, you are correct: if I start having trouble with frost heaving in my area, Al Gore is going to have some 'splaining to do.